This invention relates to an imaging element containing a blocked photographically useful compound such as a developing agent.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure (129(1975) pp. 27-30), describes the quatemary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving xcex2-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
The incorporation of blocked developers in photographic elements is typically carried out using colloidal gelatin dispersions of the blocked developers. These dispersions are prepared using means well known in the art, wherein the developer precursor is dissolved in a high vapor pressure organic solvent (for example, ethyl acetate), along with, in some cases, a low vapor pressure organic solvent (such as dibutylphthalate), and then emulsified with an aqueous surfactant and gelatin solution. After emulsification, usually done with a colloid mill, the high vapor pressure organic solvent is removed by evaporation or by washing, as is well known in the art. Alternatively, solid particle (ball-milled) dispersions can be prepared using means well known in the art, typically by shaking a suspension of the material with zirconia beads and a surfactant in water until sufficiently small particle size is produced.
There remains a need for blocked photographically useful compounds with good keeping properties, which at the same time exhibit good unblocking kinetics. With respect to developing agents, it is an object to obtain a film incorporating blocked developing agents that provide good dye-forming activity and which, at the same time, yield little or no increased fog and/or provide little or no decrease in Dmax after storage.
In one application of the invention, it is a further object to obtain blocked photographically useful agents for use in photothermographic color films. With respect to developing agents, there is a continuing need for photothermographic imaging elements that contain a developing agent in a form that is stable until development yet can rapidly and easily develop the imaging element once processing has been initiated by heating the element and/or by applying a processing solution, such as a solution of a base or acid or pure water, to the element. A completely dry or apparently dry process is most desirable. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
Similarly, there is a need for incorporating other photographically useful compounds into a photothermographic element such that they remain stable until processing and are then rapidly released. Such photographically useful compounds include, couplers, dyes and dye precursors, electron transfer agents, development inhibitors, etc., as discussed more fully below. The blocking of other photographically useful compounds, besides developing agents, are disclosed in the prior art. For example, U.S. Pat. No. 5,283,162 to Kapp et al. and U.S. Pat. No. 4,546,073 to Bergthaller disclose blocked development inhibitors, and U.S. Pat. No. 4,248,962 to Lau discloses blocked couplers wherein the blocking group in turn comprises a photographically useful group.
This invention relates to a blocked compound that decomposes (i.e., unblocks) on thermal activation by a 1,2 elimination mechanism to release a photographically useful group (also referred to herein as a PUG). In a preferred embodiment, the photographically useful group is a developing agent.
In one embodiment, thermal activation preferably occurs at temperatures between about 100 and 180xc2x0 C. In another embodiment, thermal activation preferably occurs at temperatures between about 20 and 140xc2x0 C. in the presence of added acid, base and/or water.
The invention further relates to a light sensitive photographic element comprising a support and a blocked compound that decomposes on thermal activation by a 1,2 elimination mechanism to release a photographically useful group.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a blocked compound (for example, a blocked developer) that decomposes on thermal activation by a 1,2 elimination mechanism to release a photographically useful group to form a developed image, scanning said developed image to form a first electronic image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, digitizing said first electronic record to form a digital image, modifying said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a blocked compound that decomposes by a 1,2 elimination mechanism to release a photographically useful group on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
The improvements were achieved by a compound represented by compound in which a six-membered heteroaromatic ring is present in Structure I: 
wherein:
PUG is a photographically useful group;
LINK 1 and LINK 2 are linking groups;
TIME is a timing group;
1 is 0 or 1;
m is 0, 1, or 2;
n is 0 or 1;
1+nxe2x89xa70;
t is 0,1, or 2;
T is independently selected from a substituted or unsubstituted (referring to the following T groups) alkyl group, cycloalkyl group, aryl, heterocyclic group, an inorganic monovalent electron withdrawing group, or an inorganic divalent electron withdrawing group capped with an R13 (or with an R13 and R14 group), preferably capped with a substituted or unsubstituted alkyl or aryl group; or T is joined with R11 or R12 to form a ring when T is an alkyl, aryl, or heterocyclic group; t is 0, 1, or 2, and when t is not 2, the necessary number of hydrogens are present instead;
R13 is hydrogen, or a substituted or unsubstituted alkyl, cycloalkyl, aryl or heterocyclic group;
a is 1 or 2;
A is carbon (and then a is 1) or sulfur (and then a is 1 or 2);
b is 1 or 2;
R11 is hydrogen, or a substituted or unsubstituted alkyl, cycloalkyl, aryl or heterocyclic group or R11 can combine with T to form a ring; and
B is of Structure II: 
wherein xe2x80x9cixe2x80x9d nitrogen atoms, xe2x80x9cjxe2x80x9d nitrogen oxide groups (N+xe2x80x94Oxe2x88x92), and xe2x80x9ckxe2x80x9d CR12 groups combine to form a six-membered heteroaromatic ring; xe2x80x9cixe2x80x9d is 0, 1 or 2; xe2x80x9cjxe2x80x9d is 0 or 1; the sum of xe2x80x9cixe2x80x9d and xe2x80x9cjxe2x80x9d is 1 or 2; k is 4 or 5 and the sum of i, j, and k is 6; the k R12 groups are independently selected from hydrogen, substituents and, only once, a bond joining the six-membered heterocyclic ring with A, wherein the substituents are hydrogen, alkyl, aryl, heterocyclic group, halogen, cyano, nitro, alkoxy or any other substituent, provided that such substituent does not interfere with the functioning of the blocking group; or R12 can combine with R11 to form a ring; additionally, two R12 substituents on adjacent carbon atoms can join to form a fused ring.
Preferably, T is an inorganic group such as halogen, xe2x80x94NO2, or xe2x80x94CN, when it is monovalent. When T is divalent, it preferably is an inorganic electron withdrawing group capped by R13 (or by R13 and R14 ), for example xe2x80x94SO2R13, xe2x80x94OSO2R13, xe2x80x94NR13(SO2R14), xe2x80x94CO2R14, xe2x80x94COR13, xe2x80x94NR13(COR14), etc., wherein R13 and R14 are independently selected from a substituted or unsubstituted alkyl, aryl, or heterocyclic group, preferably having 1 to 6 carbon atoms. Preferably, when T is an alkyl or aryl group it is substituted with electron withdrawing groups, for example xe2x80x94CF3 and, in the case of aryl, substituted with up to seven electron withdrawing groups. Other T groups that are preferred are heteroaromatics such as thienyl or furyl.
By the term inorganic is herein meant a group not containing carbon excepting carbonates, cyanides, and cyanates. The term heterocyclic is meant to include an aromatic and non-aromatic ring containing at least one (preferably 1 to 3) heteroatoms in the ring.
If the named groups for a symbol such as T in Structure I apparently overlap, the narrower named group is excluded from the broader named group solely to avoid any such apparent overlap. Thus, for example, heteroaromatic groups in the definition of T may be electron withdrawing in nature, but are not included under monovalent or divalent electron withdrawing groups as they are defined herein.
When referring to electron withdrawing groups, this can be indicated or estimated by the Hammett substituent constants ("sgr"p, "sgr"m) as described by L. P. Hammett in Physical Organic Chemisty (McGraw-Hill Book Co., NY, 1940), or by the Taft polar substituent constants ("sgr"1) as defined by R. W. Taft in Steric Effects in Organic Chemistry (Wiley and Sons, NY, 1956), and in other standard organic textbooks. The "sgr"p and "sgr"m parameters, which were used first to characterize the ability of benzene ring-substituents (in the para or meta position) to affect the electronic nature of a reaction site, were originally quantified by their effect on the pKa of benzoic acid. Subsequent work has extended and refined the original concept and data, and for the purposes of prediction and correlation, standard sets of "sgr"p and "sgr"m are widely available in the chemical literature, as for example in C. Hansch et al., J. Med. Chem., 17, 1207 (1973). For substituents attached to a tetrahedral carbon instead of aryl groups, the inductive substituent constant "sgr"1 is herein used to characterize the electronic property. Preferably, an electron withdrawing group on an aryl ring has a "sgr"p or "sgr"m of greater than zero, more preferably greater than 0.05, most preferably greater than 0.1. The "sgr"p is used to define electron withdrawing groups on aryl groups when the substituent is neither para nor meta. Similarly, an electron withdrawing group on a tetrahedral carbon preferably has a a of greater than zero, more preferably greater than 0.05, and most preferably greater than 0.1. When more than one electron withdrawing group is present, then the summation of the substituent constants is used to estimate or characterize the total effect of the substituents.
In a preferred embodiment of the invention, LINK 1 and LINK 2 are of structure III: 
wherein
X represents carbon or sulfur;
Y represents oxygen, sulfur or Nxe2x80x94R1, where R1 is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1;
with the proviso that when X is carbon, both p and r are 1, when X is sulfur, Y is oxygen, p is 2 and r is 0;
# denotes the bond to PUG (for LINK1) or TIME (for LINK 2):
$ denotes the bond to TIME (for LINK 1) or T(t) substituted carbon (for LINK 2).